Winch

ABSTRACT

A manually powered multi-speed winch has an automatic drive disengagement upon drive reversal which is provided by an axially movable member in one drive train which in a first axial position is engageable for drive transmission through a pawl and ratchet unidirectional drive means. The drive means in its drive-transmitting condition prevents movement of the member away from that first position. Upon drive reversal the unidirectional drive means is ineffective either to transmit drive or to maintain the member in its first position and it moves axially to a second position in which the drive means are disengaged. The member is biased towards that second axial position but is manually movable to the first by a control button accessible at the outside of the winch. The button may be lockable to override the automatic disengagement.

FIELD OF THE INVENTION

This invention relates to winches of the manually powered type.

BACKGROUND OF THE INVENTION

Such winches have for some time been provided with a plurality of driveratios between their drive input and the winch drum and variousarrangements have been proposed for allowing interchange between variousdrive ratios, this interchange being achieved, at least in all the morerecent developments, automatically upon reversal of the direction of thedrive input, without further manual interference.

There are two sorts of winch to which this interchange is applied.

In a first sort the first speed ratio, the ratio of lowest mechanicaladvantage to the user, is a 1:1 drive achieved by direct action betweena handle and the drum (U.S. Pat. No. 3728914) or through a pawl andratchet drive one side of which is associated with the drum and theother side of which is associated with the drive shaft (for example,U.S. Pat. No. 3973755).

In a second sort, all the speed ratios involve drive transmissionthrough gear trains. In one line of development illustrated by U.S. Pat.Nos. 3145974 and 4054266 automatic change is provided by means of amovably-mounted traveller gear which is engageable between coplanartransmission pinions while they are rotating in one direction but isdriven in an orbital motion out of engagement by their rotation in theopposite direction. The proposals seen in U.S. Pat. Nos. 3927580 and3998431, on the other hand, use axial movements to engage andautomatically disengage drive. In U.S. Pat. No. 3927580 drive couplingto one gear is through a dog clutch which is manually urged intoengagement but is positively driven out of engagement by face camsmoving it axially when drive is reversed. In U.S. Pat. No. 3,998,431,for a special application, a collar is axially movable to interfere withthe driving engagement between pawls on a pinion and a ratchet track onthe drive shaft, the pinion and ratchet track being both axiallystationary.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improvedautomatically ratio-changing winch of either of the sorts outlinedabove, in which a selector is operated to cause the engagement of agiven one of a plurality of drive ratios between the input and the drum,and wherein disengagement of that given ratio is automatic upon reversalof the direction of drive input. In a general embodiment of theinvention, selection of the given drive ratio is achieved by providingon a shaft a drive member which is axially moveable along the shaft, theselector means comprising means for moving the member in an axialdirection into a drive engaging first axial position whereunidirectional drive means between the shaft and the member are engaged,the member being biased away from the said position of engagement to asecond axial position where the unidirectional drive means is disengagedto uncouple drive between the shaft and the member, retention of themember in its drive-transmitting position being assured by theunidirectional drive means itself so long as drive continues to betransmitted therethrough between the member and the shaft. One side ofthe unidirectional drive means moves axially with the member, beingassociated with it.

Preferably the selector means includes a stirrup engaging a groove onthe member and which is pivotally mounted to a frame of the winch,actuation of pivotal movement of the sturrup being by means of a pushbutton accessible to the exterior of the winch. The selector means mayfurther include a lock whereby by a manual operation the member may beretained in its drive engaging position despite reversal of direction ofdrive input.

Unidirectional drive means particularly conveniently achieving therequired characteristics comprise a pawl and ratchet track arrangementwith one on the shaft and one on the member. When the ratchet track ison the shaft and a pawl is on the pinion the ratchet track will beadjacent an untoothed cylindrical portion of shaft of a diametersubstantially equal to that maximum diameter of the ratchet teeth. Then,as the pawls click over the maximum diameter of the ratchet teeth whendrive is reversed they are free to move onto the cylindrical portion ofthe shaft. This, under the influence of the biassing means, permitsmovement of the member to its drive disengaging position where the pawlsare held free of the ratchet teeth.

In one preferred embodiment the member is a pinion forming part of agear drive train, being permanently enmeshed with a next pinion in thattrain in any axial position; in another preferred embodiment the memberis a coupling sleeve permanently enmeshed with a second shaft coaxialwith the said first shaft, to transmit drive between the shafts in a 1:1ratio.

DESCRIPTION OF THE DRAWINGS AND OF PREFERRED EMBODIMENTS

A preferred embodiment of the invention will now be described withreference to the accompanying drawings wherein:

FIG. 1 is a diametrical section embodiment of winch,

FIGS. 1a and 1b are scrap sections from FIG. 1 but showing two otherconditions of the movable pinion and unidirectional drive,

FIG. 2 is a radial section to show an intermediate stage of the geartrain,

FIGS. 3a and 3b are side and plan views respectively of a selector fork,

FIG. 4 is a side view of a movable pinion,

FIG. 5 is a partial diametrical section through a second embodiment,

FIG. 6 is a side view of part of the said embodiment,

FIG. 7 is a top view of part of the embodiment on the arrow VII of FIG.5 and

FIG. 8 is a side view partially cut away of another portion of theembodiment.

The winch as seen in FIG. 1 is for manual operation and has a centraldrive shaft 1 which at its middle portion is supported by a rollingcontact bearing 2 within a cylindrical sleeve 3. The cylindrical sleeveforms an extension of a flange plate 4 which, together with a base 5 towhich it is secured at the top of the latter, forms a stationaryframework for the winch. At its uppermost end the sleeve 3 is splined toextension sleeve 6 and these two are axially keyed together by key 7.The extension sleeve 6 forms a centralising bearing for the driveshaft 1. Baseplate 5 is fast with a raised central portion 5' whichoffers a support for gearing on an extension head of the main driveshaft 1 and for intermediate gearing of the drive transmission trains aswill be described more fully later.

Primarily however axial movement of the drive shaft 1 is prevented bykeys 8 engaging a groove 9 in that shaft and entering through windows inextension sleeve 6, being held radially by a keeper ring 10 at the outersurface of the latter.

The winch drum 11 has at the inner periphery of its lower edge aninternal gear 12 and at its upper edge it is secured by three bolts 13(only one being shown) to a lower jaw plate 14 of a self-tailing channel19. In turn there is secured to the lower jaw 14 of the channel an upperjaw 15, by means of three bolts 16 (only one being shown).

Entrapped between the lower and the upper jaws 15,14 is a slip ring 17which defines a cylindrical base surface 18 of self-tailing channel 19.At one position around the periphery of ring 17 a stripper tongue 20projects and enters into a vertically extending, inwardly concavechannel 21 at the back of the stationary line guide arm 22 which isintegral with a top plate 23 which is splined at 24 to an uppermost partof the extension sleeve 6. The line guide has at its lower end anoutwardly turned, inclined, line guide 25 which is to guide and assistthe transition of line from the surface of the drum 11 into theself-tailing channel 19. A flanged washer 26 is interposed between thestationary top plate 23 and the rotating upper jaw 15, and the top.[.cao.]. .Iadd.cap .Iaddend.27 is secured by bolts 28 to the top plateand, by entrapping between itself and the top plate 23 a split collar 29which is housed in a groove in the extension sleeve 6, assures axialpositioning of itself and the top plate.

To permit rotation of the drum 11 and the jaws 14,15, rolling contactbearings 30 surround the outer circumference of the sleeve 3 and fitwithin inner sleeve 31 integral with the drum, and within an upperflange 32 of the drum.

Drive is transmittable between the central drive shaft 1 which has afacetted blind bore for the reception of a stub key from a drive handle,by means of any one of three geared drive transmission trains, all ofdifferent drive ratios and being successively engageable upon successivereversals of the direction of turning of the drive shaft so as totransmit between that shaft and the drum successively lower drive ratiosi.e. successively higher mechanical advantages. A first and lowestmechanical advantage drive train is provided by pinion 35 which isaxially movable upon the drive shaft, being borne on an extension head36 of the shaft splined at 37 to the lower end of the main portion ofthe drive shaft 1 and of complex formation which will be described laterin more detail.

Pinion 35, in whatever axial position, meshes with pinion train 38 on anintermediate complex gear 39 mounted on intermediate shaft 40 as is seenin FIG. 2. Gear 39 includes another series of integral gear teeth 41 andalso provides a support for a gear ring 42 which is engageable withcomplex gear 39 by unidirectional drive means in the shape of a pawl 43on the gear 39 and ratchet teeth 44 upon the inner periphery of the ring42. Gear ring 42 meshes at all times with gear teeth 45 formed on theextension head 36. Teeth 41 however mesh permanently with gear ring 46which is rotatably borne on a second intermediate gear shaft 33, FIG. 1.The teeth of gear ring 46 mesh permanently not only with teeth 41 ongear 39 but also with geared teeth of a gear ring 47 which is rotatablymounted to the extreme base of the extension head 36 and coupled to thathead 36 through a unidirectional drive made up of pawls 48 in the headand ratchet teeth 49 on the inner periphery of the ring 47. These pawlsare held in position in the housing and axial position of the ring 47 isassured by end cap 56 secured by screw 50 to the extreme end of the head36.

The final element of all the gear drive trains is a transmission sleeve51 mounted, through rolling contact bearings 52, on the second gearshaft 33 and which has at its uppermost end gear teeth 53 whichpermanently mesh with the internal gear teeth 12 on the drum.

Gear ring 46 is the sole source of drive input to the transmissionsleeve 51 and is coupleable to that sleeve by means of unidirectionaldrive formed by pawls 54 in the gear ring 46 and ratchet teeth 55 formedat the lowermost end of the transmission sleeve 51. The effect of theunidirectional drive 54,55 is to uncouple from any part of the geardrive transmission trains beyond that drive the effect of anyoverrunning of the winch drum. It has the effect of making all theautomatic transmissions which are about to be described entirelyindependent of overrunning by the drum and controlled only by thosefactors which are about to be described.

The first drive train that of highest drive transmission between thedrive input shaft and the drum and therefore of lowest mechanicaladvantage is that formed by pinion 35, pinion 38, pinion 41, gear ring46 and then, in common with all the other drives, transmission sleeve51, gear teeth 53 and internal gear 12.

The second drive train, of intermediate mechanical advantage, includesring 47 and gear ring 46.

The third train and that of greatest mechanical advantage includes teeth45, ring 42, gear 41 and ring 46.

The successive trains have successively odd and even numbers of gears inthem and also have successively oppositely opposed unidirectional drivesin them (namely in the first train pawls 60 in pinion 35 with ratchetteeth 61 on drive shaft 1, in the second train pawls 43 with ratchetteeth 44 on gear ring 42 and in the third train pawls 48 and ratchet49).

Thus successive rotation of the drive input shaft in opposite directionswould cause transmission of drive successively through different driveratios. However, if means are not found for disconnecting the first ofthese drives (that of lowest mechanical advantage) then it will alwaysbe preferentially engaged in a given direction of rotation of the maindrive shaft, since it will cause a rotation of the gear ring 47 in thethird train in a sense that it is overtaking the extension head 36 andis merely clicking past the ratchet teeth 49 on it. Means are thereforeprovided for the automatic self-disengagement of the pinion 35 upon afirst reversal of drive and these will be described in more detail now.

As has been mentioned the pinion 35 is axially movable on the driveshaft of which the head 36 forms part. Head 36 has a smooth cylindricalsurface 65 upon which is rotatably borne a smooth cylindrical surface 66of the pinion 35.

The pawls 60 are housed in pawl housings 67 at an uppermost part of thecylindrical surface 66, being held axially in position by a cover plate64 (FIG. 1). Level with a lower portion of the cylindrical surface 66and in the outer periphery of the pinion 35 there is formed a channel 68which is continuous around that circumference and which is engaged bypins 69 directed inwardly from legs 70 of a fork 71 best seen in FIG. 3.The fork 71 is mounted upon a bracket 72 fixedly secured to the flange 4and is pivoted to the bracket by a pin 73 passing through a bore 74 inthe base of the fork. The fork has an actuating arm 75 extending at anangle to the legs 70, and this has a small aperture 76 for the receptionof an end hook of a tension spring 77 of which the other end is anchoredin the bracket 72. The effect of the pivotal mounting of the stirrup isthat with pins 69 permanently engaged in channel 68 on the pinion 35 thepivoting can in principle cause axial movements of the pinion 35 alongthe drive shaft. An uppermost axial position is defined by abutment ofthe cover plate 64 against a washer 78 entrapped between ratchet teeth61 and the bottom of the cylindrical sleeve 3, and a lower limitposition of travel is defined by abutment of an undercut ledge 79 (FIG.4) in the gear 35 with a flange 80 on the extension head 36. The effectof the tension spring 77 is to bias the stirrup towards clockwiserotation and hence to bias the pinion 35 towards its lower limitingposition. The diameter of the cylindrical part 65 of the drive shafthead is substantially equal to the maximum diameter of the ratchet teeth61. Thus, if the pawls 60 are clicking over the ratchet teeth 61 theirinnermost edges 62 will be at the same diameter as that of thecylindrical surface 65 and they will be free to transfer downwardly tothe cylindrical surface 65. This condition is seen in FIG. 1b, where thepinion 35 is free to move axially in the direction of the arrow A. Thatthis movement will happen when the occasion arises is assisted by thebiasing due to the spring 77 (although sufficient biasing may beavailable by the action of gravity alone). This lowermost axial positionof the pinion is seen in full lines in FIG. 1. However, when the pinion35 has been moved to its uppermost position indicated in dotted line inFIG. 1 and seen more clearly in FIG. 1a, the pawls 60 are fullyengageable between the ratchet teeth 61 and their innermost edges 62penetrate inwardly further than the diameter of the cylindrical surface65. Thus while they remain engaging between the teeth 61 their axiallylowermost edge face abut against a lowermost shelf surface 63 at thefoot of those teeth 61 and which is provided by an uppermost planarsurface of the head 36. While they are so engaged downward movement ofthe pinion 35 is impossible whatever the biasing.

To cause the pinion to be moved to its uppermost position in which pawls60 can engage with and penetrate between teeth 61 an actuating pushbutton is provided which has a stem 89 and lock nuts 81 and 82 on ascrewthreaded extension of the stem 89. Lock nut 82 has a rounded noseand abuts against a surface 83 of the arm 75. The stem 89 is axiallymoveable in a sleeve housing 84 secured to the base 5, and at its endoutside the sleeve it is secured to a readily visible and accessiblepush button head 85. Screw 86 penetrates radially through the housing 84and its end engages in a slot 87 in the stem 89 to define the limits ofmovability of the stem. A spring 88 is trapped between the end of thehousing 84 and a washer behind the lock nut 81 and urges the stem 89inwardly, but this spring is much weaker than spring 77 and isoverridden by it.

To engage therefore the first drive train, the user of the winch pressesthe button 85 inwards causing rotation of the fork in an anti-clockwisedirection against the biassing of the sleeve 77, moving the pinion 35 toits uppermost position in which the pawls 60 are free to enter betweenthe ratchet teeth 61. Once this position has been established the useris free to release pressure on the button 85 since as has beendescribed, because the pawls remain engaged, the pinion will be held inits drive-engaging position for so long as drive is being transmittedthrough it upon appropriate rotation of the drive shaft 1.

When however the drive is reversed drive is established through thesecond gear train 45, 42, and a backward rotation will be imposed (backthrough gear 38) upon the pinion 35 which will therefore rotate in theopposite direction of the shaft 1 and its pawls 60 will click over theteeth 61 and thereby become free to slide onto the cylindrical surfaces55 and cause their own permanent disengagement as the pinion movesdownwardly down that surface under the influence of gravity and of thetension spring 77.

A further reversal of the drive shaft will cause not re-engagement ofthe first drive, since the pawls are still held free of the teeth 61,but will cause engagement of the third drive via gear ring 47 and ring46.

The user may wish that upon any second reversal he will in fact revertto first drive ratio. In this case a lock can be provided upon theselector by virtue of a transverse extension 90 of the slot 87. Then,the user having depressed the push button inwardly gives it a quarterturn so that the end of the screw 86 is engaged in the L-shapedextension 90 and the push button is held locked in its inner position,in which teeth 60 and ratchet 61 are permanently engageable uponappropriate drive.

A second embodiment of the invention can be seen in FIGS. 5 to 8. Thisillustrates that the principle of the invention may be applied to thesort of manually powered winch in which the lowest mechanical advantagedrive train is a 1:1 drive between the drive shaft and the drum. In thiswinch the axially movable member which causes drive transmission throughone drive train or disconnects drive transmission from that drive trainis a coupling sleeve permanently meshed with a shaft coaxial with theshaft relative to which it moves axially.

In FIG. 5 only parts associated with this different form of axialmember, and relevant to the changes made are shown since the remainderof the structure of the winch, and the selector mechanism which willoperate the axially movable member are in substance as previouslydisclosed.

In this embodiment a winch drum 100 is rotatable on a conventionalstationary frame structure schematically indicated at 101. It is securedto a top plate 102 within which is splined a ring 103 with radiallyinwardly directed ratchet teeth 104. A pawl 105 on a boss element 106can drivingly engage with the ratchet teeth in a unidirectional drive.The boss element 106 includes a cylindrical part 107 mounted throughbearing 108 inside the top end of the stationary structure 101 forrotation relative to it. A centre shaft 109 is borne within the bosspart 106 and is splined to it at 110. A retainer plate 111 is screwed tothe shaft by screw 112 and bears down on boss 106. If the shaft 109 isrotated in one direction drive will be transmitted in a 1:1 ratio fromit through the pawl 105 and ratchet 104, top plate 102 to drum 100. Ifthe drive is in the opposite direction (or if the drum is overrunningthe rotation of the shaft) the pawl will click on the ratchet teeth.

This embodiment is one in which drive is brought into the winch fromunderneath, but in principle it is identical (with appropriate reversalof unidirectional drive linkages) to that where drive is brought to thetop end of the centre shaft 109 direct from a handle.

At the lower end of the centre shaft 109 there is a widening on theouter face of which are formed ratchet teeth 115 analogous to teeth 61of the previous embodiment. A member 116 is axially slidable upon theshaft, this member being analogous to pinion 35 of the first embodimentbut differing from it in that, instead of meshing permanently withanother gear in the relevant drive transmission (gear 38, FIG. 2, of thefirst embodiment) it is permanently enmeshed by means of inwardlydirected spline teeth 117 with outwardly directed spline teeth 118 on asecond shaft 119 mounted coaxially with the centre shaft 109 androtatable relative to it. Its centering is assured by the projection ofan end journal 120 of the shaft 119 to within a hollowed out end of theshaft 109, with the interposition of bearings 121 between them.

The member 116 taking the form of a coupling sleeve between the shaft109 and 119 has mounted within it pawl 122 analogous to pawl 60 of thefirst embodiment. It has a channel 68 for engagement by a selectormechanism exactly as in the first embodiment, and a top plate 64.

It can be seen that the maximum diameter of the ratchet teeth 115, atregion 123 is just somewhat greater than the minimum diameter of achamfered-off top portion of the spline teeth 118, this portion beinggiven the reference 124 in FIG. 5. Thus, exactly as in the firstembodiment, when the member is in its axially upper position in whichpawls 122 engage between teeth 115, and drive is transmitted betweenshaft 119 and shaft 109 in the appropriate direction, drive is thustransmitted via spline teeth 118 on shaft 109 and spline teeth 117 onthe member 116 via pawl 122 on the member 116 to ratchet teeth 115 onthe shaft 109. However if the direction of drive input is reversed thepawl 122 will click over the maximum diameter of the ratchet teeth 115bringing it outwardly of the innermost diameter of the chamfered portion124 of the splines 118 so that the member 116 is free to move eitherunder gravity or under bias, exactly as described for the previousembodiment, to its lowermost position, that which is indicated in FIG.5. In this position it can be seen that pawl 122 is held outwardly ofmaximum diameter of teeth 123 by abutment on the land surface 125 (FIG.7) of the spline teeth 118 on the shaft member 119.

The shaft is seen in more detail in FIG. 6 with land surfaces 125chambers 124 and splinings 118 at end portion 120 clearly seen.

The shaft 119 also provides however a rotatable mounting for gear 126analogous to pinion 47 of the first embodiment forming part of asuccessive drive train for this multi-speed winch and which is a geartrain. A pawl mounted within recess 127 (FIG. 6) with the shaft 119forms unidirectional drive means between that shaft and ratchet teeth128 formed on the inner periphery of the pinion 126.

In the specific form being described drive is brought into this shaftcomplex by an end shaft 130 rotatably borne at the bottom end of thetotal shaft assembly in base structure 5" analogous to structure 5' ofthe first embodiment. The end shaft 130 has integrally formed in itpinion teeth 131 which (analogously with pinion 45 of the firstembodiment) form part of a yet further drive ratio, which is also a geartrain. Lower stub axle 132 of the shaft 119 is received in the hollowcentre of the end shaft 130, the two shafts 119 and 130 being lockedtogether for rotation together by interaction between plane faces 133upstanding from the axially upper edge of the pinion teeth 131 withsimilar plane faces 134 on the lower end of the shaft 119, parallel saidfaces 133 on the shaft 130 being spaced apart one on each side of adiametrical plane passing through its axis and with a gap between them,faces 134 being correspondingly formed in and spaced apart by the solidmaterial of the shaft 119.

Drive is brought into the assembly by the fitting of a key from a drivetransmission train into keyed recess 135 at the extreme lower end of endshaft 130.

In operation the selector is operated against its spring bias to movethe member axially upwardly to a position so that pawl 122 penetrates tobetween ratchet teeth 115 to transmit drive, as previously described,from shaft 119 to shaft 109 whence drive is derived via boss 106 andpawl and ratchet 105, 104 in a 1:1 ratio by winch drum 100. If thedirection of drive input is reversed the pawl 122 clicks and the member106 is free to move axially downwardly, as previously described. Thereversal brings automatically into play the next drive ratio to thedrum, through gear 131. A second reversal of the direction of driveinputs disconnects the unidirectional drive means in that drive ratioand engages, not the 1:1 drive ratio, but the third ratio--the geartrain involving gear 126. The 1:1 drive is not engaged because, asdescribed, in the lower position of the member 106 the pawl 122 is helddisengaged from ratchet teeth 115, by being held on a land surface 125of the spline teeth 118.

We claim:
 1. A manually powered winch comprising:a winch drum rotatableabout a central axis; a drive input; a plurality of drive trains ofrespectively different drive ratios between the drive input and thewinch drum; and means for causing successive driving engagement of drivetrains of successively differing mechanical advantage upon successivereversals of direction of rotation of the drive input to drive the drumin one direction of rotation, said means including a first .Iadd.axial.Iaddend.shaft, a member of said drive train being mounted .[.on.]..Iadd.coaxially for axial movement relative to .Iaddend.the shaft .[.tobe axially movable thereon.]., uni-directional drive means engageablebetween the member and the shaft and means for biasing the member awayfrom a first axial position toward a second axial position, the membertransmitting drive between the drive input and the winch drum, andselector means for moving the member axially from the second axialposition to the first axial position, in one of said axial positions theuni-directional drive means being engageable between the member and theshaft and in the other of the said axial positions the uni-directionaldrive means being disengaged between the member and the shaft, retentionof the member in the said one of the axial positions being assured bythe drive means for so long as the drive input continues in thedirection in which drive is transmitted through said drive means betweenthe member and the shaft.
 2. A manually powered winch as claimed inclaim 1 wherein the said one of the drive trains is a gear train ofleast mechanical advantage of the trains, the said member being a pinionin said gear train.
 3. A manually powered winch as claimed in claim 1wherein the said member is a coupling sleeve, and wherein said causingmeans further includes a second shaft coaxial with the said first shaft,the sleeve being permanently engaged with the second shaft for rotationtherewith.
 4. A manually powered winch as claimed in claim 1, claim 2 orclaim 3 wherein the said axis is vertical, the said first position beingthe said one of the axial positions and being above the second position,and gravity urging the member from the first to the second position. 5.A manually powered winch as claimed in claim 1, claim 2 or claim 3wherein the uni-directional drive means comprise a pawl and ratchettrack, one of the pawl and the ratchet track being on the member and theother on the first shaft, means defining a ledge at one axial end of theratchet track nearer the said other of the axial positions, a peripheraldiameter of the ledge being substantially identical with that of theratchet teeth, an edge of a pawl when engaged in the track penetratingto beyond the said peripheral diameter of the ratchet teeth whereby anend face of the pawl abuts the ledge for preventing movement of themember to the said other of the axial positions but clicking of the pawlover the peripheral diameter of the teeth moves the edge of the pawl tothe said diameter and frees the pawl from the ledge.
 6. A manuallypowered winch as claimed in claim 1 wherein the selector means includesa manually operable lock for maintaining said member in said oneposition after reversal of direction of rotation.
 7. A manually poweredwinch comprising:a winch drum rotatable about a central axis; a driveinput; a shaft; a plurality of drive trains of respectively differentmechanical advantage, each of said trains including unidirectional drivemeans for causing said trains of successively progressing mechanicaladvantage to be successively effective upon successive reversal of thedirection of rotation of the drive input, a first of the trains in thesaid succession including an axially movable member, the movable memberbeing mounted .[.on.]. .Iadd.coaxially for axial movement relative to.Iaddend.the shaft, the unidirectional drive means being operable totransmit drive between the member and the shaft only when the saidmember is in a first axial position on the shaft, the unidirectionaldrive means including means effective to maintain the member in thefirst axial position when this said unidirectional drive means is indriving engagement, motion in the unidirectional drive means in anon-drive-transmitting sense being effective to free the member from thefirst axial position, biasing means for biasing the member away from thefirst axial position to a second axial position, the said unidirectionaldrive means being inoperable when the member is in its second axialposition, and selector means manually operable to move the member to itsfirst axial position.
 8. A manually powered winch as claimed in claim 7wherein the said unidirectional drive means is at least one pawl on themember and a ratchet-toothed track on the shaft, there being a ledge inthe shaft at one axial end of the ratchet track nearer to the saidsecond position, the ledge having a maximum diameter substantially thesame as the maximum diameter of the teeth of the ratchet track, and asmooth, untoothed, portion of the shaft terminating axially at theledge.
 9. A manually powered winch as claimed in claim 8 wherein theselector means includes a fork, a pivotal mounting for the fork, meanson the fork engaging an annular groove in the member, a push buttonmovable along its own axis and accessible outside the winch, a pivotalconnection between the push button and fork, movement of the push buttoninwardly of the winch pivoting the fork to move the member axially toits first axial position, and spring means acting on the fork to biasthe fork against the said movement.
 10. A manually powered winch asclaimed in claim 9 wherein the push button is rotatable about its ownaxis and means effective in one rotated position to hold the buttonlocked in its inward position. .Iadd.
 11. A manually powered winchcomprising:a winch drum rotatable about a central axis; drive input; atleast first, second and third drive trains of respectively differentdrive ratios between the drive input and winch drum; means for causingsuccessive driving engagement of said second drive train anddisengagement of said first drive train upon a first reversal ofdirection of rotation of the drive input and driving engagement of saidthird drive train and disengagement of said second drive train upon asecond reversal of direction of rotation of the drive input to drive thedrum in one direction of rotation; and means unaffected by a firstreversal of the direction of rotation of the drive input engaging saidcausing means and operable to override and prevent the engagement ofsaid third train by said causing means so that said first train isengaged upon said second reversal of direction of the drive input..Iaddend.